High pressure discharge lamp

ABSTRACT

The invention relates to a high-pressure discharge lamp whose discharge tube mainly consists of ceramic material. According to the invention a compartment is present at at least one end of the discharge tube while a wall of this compartment screening at least part of an adjacent electrode consists of ceramic material. The said wall is preferably part of a sealing member of the discharge tube.

" United States Patent Timmermans July 1, 1975 [54] HIGH PRESSUREDISCHARGE LAMP 2,982,877 5/1961 Geldern 313/205 X 3,358,167 12/1967Shanks [75] Inventor Abraham T'mmel'mans, Emdhoven 3,519,864 7/1970Gungle et a1. 313/25 Netherlands [73] Assignee: U.S. PhilipsCorporation, New

York, Przmary ExammerSaxfield Chatmon, Jr.

Attorney, Agent, or Firm-Frank R. Trifari [22] Filed: Jan. 22, 1974 [21]Appl. No.: 435,534

[57] ABSTRACT [30] Foreign Application Priority Data Feb. 16, 1973Netherlands 7302172 The invention relates to a higlrpressure dischargelamp whose discharge tube mainly consists of ceramic 52 us. c1. 313/318;174/505; 313/17; material- 313/25; 313/205; 339/144 R According to theinvention a compartment is present [51] Int. Cl HOlj 5/48; HO lj 5/50 atat least one end of the discharge tube while a wall [58] eld 0 Search ofthis compartment screening at least part of an 313/205, 208, 8; adjacentelectrode consists of ceramic material. The said wall is preferably partof a sealing member of the [56] References Cited discharge tube.

UNITED STATES PATENTS 2,561,898 7/1951 Willoughby 313/205 X 7 Claims, 10Drawing Figures 3,892,993 SHEET 2 10 11 14a 16 14 15 13 1011 14c 16 1415 12 I 1 1 1 1 1 1 1 1 1/ 1 j 1 Vi l I [\Q 11/ x7 7 Fig. 2 Fig. 3

Fig.5

1 1 1 1 1 1 I /f "l 11 /1 1 H I V T.

SHEET Fig- Fig

HIGH PRESSURE DISCHARGE LAMP The invention relates to a high pressuredischarge lamp provided with a discharge tube whose filling coniprisesat least a metal in which the wall of the discharge tube mainly consistsof ceramic material and in which an electrode is prescntin the dischargetube nearboth ends, a compartment being present between atleast one ofthe electrodes and the adjacent end of the discharge tube, whichcompartment is in fluid communication with the part of the dischargetube in which the discharge is effected, a wall of said compartmentscreening at least part of an adjacent electrode from the interior ofsaid compartment.

In this connection ceramics (or ceramic material) is understood to meanpolycrystalline material such as, for example, densely sinteredaluminium oxide or beryllium oxide and monocrystallinc material such as,for example, sapphire.

A known high-pressure discharge lamp of the kind mentioned in thepreamble is described, for example, in U.S. Pat. 3,422,300. A drawbackof this known lamp is that the wall of the compartment screening part ofan adjacent electrode consists of a metal disc which is mounted on anelectric lead-through conductor of this electrode. This is a drawbackbecause the assembly of electrode and lead-through is rather wide. Thisleads to less freedom during manufacture in the advance provision ofsealing members or screening members near the end of the discharge tube.

An object of the invention is to provide a high pressure discharge lampin which there is great freedom in the provision ofsealing members orscreening members near an end of the discharge tube before the electrodesystem is provided.

According to the invention a high pressure discharge lamp provided witha discharge tube whose filling comprises at least a metal and in whichthe wall of the discharge tube mainly consists of ceramic material andin which an electrode is present in the discharge tube near both ends,and in which a compartment is present between at least one of theelectrodes and the adjacent end of the discharge tube, which compartmentis in free communication with the part of the discharge tube in whichthe discharge is effected, and in which a wall of said compartmentscreens at least part of the adjacent electrode from the interior ofsaid compartment is characterized in that the wall of the compartmentwhich screens at least part .of the electrode is likewise made ofceramic material and that said wall forms a part of an entirely ceramicmemberwhich is secured to the wall of the discharge tube in agastightmanner.

An advantage of this lamp is that. ceramic sealing members or screeningmembers may be provided in advance near the end of the discharge tubeand this before placing the electrode system in the discharge tube.

An advantage of the compartment is that it can be used as a reservoirfor the metal, for example, mercury or an amalgam in the discharge tube.This prevents an irregular glowing of the are near the electrode. Suchan irregular glowing in a lamp without a compartment may be caused bytemperature fluctuations of the electrode caused by quickly evaporatingdrops of metal or drops of, for example, a metal compound in thevicinity of this electrode.

The ceramic member may be, for example, a member which does not have ascaling function of the discharge sures in the first place the screeningof the interior of the compartment against radiation from the adjacentelectrode and in the second place it serves or also serves for sealingthe discharge tube.

. The screening wall of the compartment may consist of, for example, aceramic part having a flat shape.

In a further preferred embodiment of a high pressure discharge lampaccording to the invention the wall of the compartment screening atleast part of the electrode consists of a collar-shaped bulge of thesealing member. 7

An advantage of this preferred embodiment is that a compartment can beobtained which is rotation symmetrical with respect to, for example, thelead-through for the electrode. This has the advantage that there isgreater freedom in the choice ofthe operating positions of the dischargelamp.

The latter preferred embodiment may further be improved by providing thebulge near the adjacent electrode with a flanged thickened part.

An advantage thereof is that the compartment is better sealed from thespace in the discharge tube in which the discharge is effected. Theadvantage is namely that there is less risk of a detrimental influenceof metal drops near the electrode on the discharge.

In a further preferred embodiment of a high pressure discharge lampaccording to the invention the compartment is substantially entirelybounded by an inner wall of a recess in the entirely ceramic member.

An advantage of this preferred embodiment is that such a compartment canbe obtained in a very simple manner. It may consist of, for example,drilling a hole in the ceramic member. In that case care is to be takenthat the axis of this recess runs at most parallel to the axis of thedischarge tube, or otherwise constitutes an acute angle with theadjacent alignment of this discharge tube. Otherwise asatisfactoryscreening of the radiation from the adjacent electrode cannot beobtained.

in a further preferred embodiment ofa high pressure discharge lampaccording to the invention, the free connection between the compartmentand the part of the discharge tube in which the discharge is effectedhas the shape of a ring which is bounded at one end by an electricsupply conductor to the adjacent electrode and at the other end by thewall of the compartment which screens at least part of the electrode.

An advantage of this preferred embodiment is that the temperature of thecompartment in which generally the lowest temperature of the dischargetube occurs can easily be controlled and this because this compartmentis farther remote from the adjacent electrode.

In an improvement of'the latter preferred embodiment of a high pressuredischarge lamp-according to the invention in which also a second ceramicmember is present which is connected at least in a gastight manner tothe first ceramic member the compartment consists ofa recess in at leastone of the two ceramic members, which recess is located on the side ofthe annular free connection remote fromthe adjacent electrode. Anadvantage of this embodiment is that a compartment having very defineddimensions can be manufactured. This is important in connection with thecompensation of the spread amongst discharge tubes of one and the sametype.

In the latter improvement the recess may be entirely located in thefirst ceramic member or entirely in the second ceramic member or partlyin the first ceramic member and partly in the second ceramic member.

The invention will further be described with reference to a drawing.

FIG. 1 is a perspective view of a discharge lamp according to theinvention;

FIG. 2 is a longitudinal section through an end of the discharge tube ofthe lamp of FIG. 1;

FIG. 3 is a first modification of the sealing of the discharge tube;

FIG. 4 is a second modification of the sealing of the discharge tube;

FIG. 5 is a third modification of the sealing of the discharge tube; 1

FIG. 6 is'a fourth modification of the sealing of the discharge tube;

FIG. 7 is a fifth modification of the sealing of the discharge tube;

FIG. 8 is a sixth modification of the sealing of the discharge tube;

FIG. 9' is-a seventh modification of the sealing of the discharge tube;

FIG. l0'isan eighth modification of the sealing of the discharge tube.

In FIG. l-,1 denotes a discharge tube of a high pressure sodium vapourdischarge lamp of 400 Watts. 2 denotes the outer envelope of thisdischarge lamp. 3 denotes the lamp cap. 4 denotes a terminal wire.

In FIG. 2, I0 denotes part of the discharge tube 1 of FIG. lrThisdischarge tube is made of densely sintered aluminium oxide. This tubemay alternatively be made of, for-example, sapphire. The filling of thetube con- "sistsof an amalgam, namely a combination of sodium andmercury and also contains an ignition gas, for example,xenon. I1 denotesan electrode which is secured through a connection piece 12 to a tubularelectric supply condu'ctor'13 of, for example, niobium. A first entirelyceramic sealing member is denoted by 14. A second cover-shaped ceramicsealing member is denoted by the reference numeral 15. The first sealingmember 14 is provided with a collar-shaped bulge which is denoted byl4a. In this manner an annular compartment 16 is formed between thisbulge 14a and the adjacent part of the discharge tube 10, and thegreater part of this compartment is screened by the wall 14a from theadjacent electrode 11. The parts I4, 15 and 10 are connected, forexample, in a manner as described in Netherlands Pat. .Application No.6,704,681. A slightly fatter line denotes a sealing glass in the FIG. 2,etc..

FIG. 3 uses the same reference numerals as FIG. 2. The differenceis,however, that a bulge 14c is used which relative .to the bulge l4dofFIG. 2 is shifted to the electrode 11. An advantage of this embodimentis that the compartment 16 between the bulge 14c and the adjacent partof the discharge tube 10 has become larger so that more amalgamcan beaccommodated therein. 7

FIG. 4 shows a modification which only deviates in one detail from thatof FIG. 3. In this case a flanged part 14d has been added to the bulge140, which part is at right angles to the longitudinal axis of thedischarge tube. Consequently, the compartment 16 can still better besealed from the rest of the discharge space which is located on theelectrode side of the ceramic bulge.

FIG. Sshows a further modification in which the sealing member of thedischarge tube 10 again consists of two parts namely a first sealingmember and a second sealing member 31. The member 30 has the shape of astud and 31 is shaped as a cover. In the modification of FIG. 5 theelectrode is denoted by 33 and the tubular supply conductor of thiselectrode is denoted by 34. The member 30 is provided with a recess 36and this on the side of an annular opening 35, between part 30 and thesupply conductor 34, which side is remote from the electrode 33.

In the modification of FIG. 6 whose reference numerals are the same asthose of the previous FIG. 5 the cover-shaped sealing member 31 also hasa recess which adjoins the recess in the sealing member 30. Thecompartment 36 is therefore larger in the case of FIG. 6 than that ofFIG. 5. In the modification of FIG. 6 relatively more amalgam cantherefore be accommodated in the compartment.

In FIG. 7 the compartment 36 is entirely present in the ceramic member31. The ceramic member 30 has no recess. Only the annular openingbetween the member 30 and the lead-through conductor 34 can be seen. InFIG. 8 a first sealing member 44 is secured to the end of the dischargetube 10. 45 denotes the second sealing member. 46 denotes the electrodeand 47 is the electrical lead-through. The compartment 48 in thismodification again partly consists of a recess in the ceramic member 44and partly of a recess in the second ceramic member 45.

FIG. 9 shows that a modification is possible in which the sealingmembers 54 and 55 are not directly connected together but are connectedtogether through part of the wall of the discharge tube 10. 57 is aceramic member connected to part 54. 58 denotes the compartment.

Finally FIG. 10 shows a modification with two sealing members 64 and 65which are connected together and to the discharge tube 10 in the samemanner as shown with reference to FIG. 2. The member 64 has a recess 68representing a compartment. It is of course feasible that more similarcompartments are present in the member 64 such as is represented, forexample, by the part 69 shown in broken lines. Likewise it is possiblefor the compartment in the member 64 to consist of a circular groove.

What is claimed is:

1. A high-pressure discharge lamp having a first electrode and a secondelectrode and an elongated cylindrical discharge tube having a fillingwhich comprises a metal, said discharge tube having a wall whichconsists primarily of ceramic material, the first electrode beingdisposed at a first end of the discharge tube and the second electrodebeing disposed at a second end of the discharge tube, a wall defining acompartment between at least one of the electrodes and the adjacent endof the discharge tube, the compartment being in fluid communication withthe part of the discharge tube in which the discharge is effected, saidwall screening at least part of an adjacent electrode from the interiorof said compartment, wherein the portion of wall of the compartmentscreening at least part of the electrode is made of ceramic material,said wall constituting a part of an entirely ceramic member which issecured to the wall of the discharge tube in a gastight manner.

2. A high-pressure discharge lamp as claimed in claim 1, wherein saidceramic member is a sealing member for the end of said discharge tubewhich is secured in a gastight manner about an entire axial portionthereof.

3. A high-pressure discharge lamp as claimed in claim 2, wherein thewall of the compartment screening at least a part of the electrodecomprises an axially extending annular bulge of said sealing member.

4. A high-pressure discharge lamp as claimed in claim 3, wherein saidannular bulge has a radially extending flange disposed at one axialportion thereof.

5. A high-pressure discharge lamp as claimed in claim 2, wherein saidcompartment is substantially entirely bounded by an inner wall of arecess in the entirely ceramic member.

6. A high-pressure discharge lamp as claimed in claim 2, in which thefluid connection between the compartment and the part of the dischargetube in which the discharge is effected has an annular shape which isbounded at one axial extremity by an electric supply conductor which isconnected to the adjacent electrode and at the other axial extremity bythe portion of said wall of the compartment which screens at least partof the electrode.

7. A high-pressure discharge lamp as claimed in claim 6 furtherincluding a second ceramic member which is connected at least in agas-tight manner to the first ceramic member, and wherein saidcompartment consists of a recess in at least one of the two ceramicmembers, said recess being disposed on the axial side of the annularfluid connection most remote from the adjacent electrode.

1. A high-pressure discharge lamp having a first electrode and a secondelectrode and an elongated cylindrical discharge tube having a fillingwhich comprises a metal, said discharge tube having a wall whichconsists primarily of ceramic material, the first electrode beingdisposed at a first end of the discharge tube and the second electrodebeing disposed at a second end of the discharge tube, a wall defining acompartment between at least one of the electrodes and the adjacent endof the discharge tube, the compartment being in fluid communication withthe part of the discharge tube in which the discharge is effected, saidwall screening at least part of an adjacent electrode from the interiorof said compartment, wherein the portion of wall of the compartmentscreening at least part of the electrode is made of ceramic material,said wall constituting a part of an entirely ceramic member which issecured to the wall of the discharge tube in a gastight manner.
 2. Ahigh-pressure discharge lamp as claimed in claim 1, wherein said ceramicmember is a sealing member for the end of said discharge tube which issecured in a gastight manner about an entire axial portion thereof.
 3. Ahigh-pressure discharge lamp as claimed in claim 2, wherein the wall ofthe compartment screening at least a part of the electrode comprises anaxially extending annular bulge of said sealing member.
 4. Ahigh-pressure discharge lamp as claimed in claim 3, wherein said annularbulge has a radially extending flange disposed at one axial portionthereof.
 5. A high-pressure discharge lamp as claimed in claim 2,wherein said compartment is substantially entirely bounded by an innerwall of a recess in the entirely ceramic member.
 6. A high-pressuredischarge lamp as claimed in claim 2, in which the fluid connectionbetween the compartment and the part of the discharge tube in which thedischarge is effected has an annular shape which is bounded at one axialextremity by an electric supply conductor which is connected to theadjacent electrode and at the other axial extremity by the portion ofsaid wall of the compartment which screens at least part of theelectrode.
 7. A high-pressure discharge lamp as claimed in claim 6further including a second ceramic member which is connected at least ina gas-tight manner to the first ceramic Member, and wherein saidcompartment consists of a recess in at least one of the two ceramicmembers, said recess being disposed on the axial side of the annularfluid connection most remote from the adjacent electrode.